Method of making media of controlled porosity

ABSTRACT

A method of making a non-woven fibrous media, combining high vapor permeability and low liquid permeability, includes the steps of providing a non-woven fabric formed from fibers that are prematurely crystallized during fabric formation and have a wide heat of fusion range distribution, and calendering the fabric to soften the small polymer crystals therein of low heats of fusion, but not the relatively larger polymer crystals therein of relatively higher heats of fusion, thereby to retain high vapor permeability while providing low liquid permeability. The polymer is preferably isotactic polypropylene.

BACKGROUND OF THE INVENTION

The present invention relates to a method of making fibrous media ofcontrolled porosity, and more particularly such a media which combineshigh vapor permeability and low liquid permeability, and the productthereof.

It is well known to produce a laminate made from various polymers andtextiles for use in a wide variety of product applications. For example,meltblown and spunbond materials afford a high level of vaporpermeability and liquid permeability when used either by themselves orin combination with one another and/or other porous materials.

Meltblowing is a method for economically producing very small fiberswhich are mostly suitable for filtration and insulation applications.Fibers smaller than 1 micron in diameter may be produced by meltblowing,and the average fiber diameter in conventional meltblowing is about 4microns, with fiber size distribution ranging from ¼micron to 8 microns.To form such small fibers one must start with polymer resins of very lowmolecular weight. In this process the nonwoven fabric is formed in onestep from the polymer resin into the final meltblown nonwoven fabric.

In contrast, spunbonding is very similar to conventional fiber spinningwhere several processing steps are required to form the spunbond fabric.Spunbond fibers go through a drawing stage and then a laydown stagewherein the drawn fibers are laid down into a matt and the matt is thenbonded by a thermobonding calender or mechanical entangling to form thenonwoven fabric. The resins used in the spunbonding process have lowermolecular weight than those used in the conventional melt spinningprocess and higher molecular weights than those used in the conventionalmeltblowing process. Fibers smaller than 10 microns in diameter are verydifficult to produce economically by spunbonding, and the average fiberdiameter for conventional spunbonding processes is about 18 microns.

However, for particular applications, such as those in the health careindustry—e.g., infant diapers, sanitary pads, adult incontinence wear,medical surgical dressings, and the like—the laminate must perform threedistinct functions: First, a topsheet intended to contact the patient'sskin must allow the passage of moisture (e.g., blood, urine and likeliquids) therethrough while at the same time providing an acceptablefeel to the wearer's skin. Second, an absorbent core, intermediate thetopsheet and the backsheet, must be capable of absorbing the moisturewhich has been received through the frontsheet. Third, a backsheet, onthe back of the absorbent core, prevents leakage of moisture outwardlyof the laminate. The present invention relates specifically to thebacksheet component.

The barrier properties of the backsheet (i.e., the trapping of moistureand other liquids) are typically achieved by incorporating into thebacksheet a plastic layer or film which acts as a moisture barrier.Various major disadvantages associated with the utilization of suchbarrier films are the low moisture vapor transmission rates (MVTR) ofthe barrier films, undesirable crinkling noise created by the barrierfilm during usage of the product, and a stiffening of the product (dueto the barrier film) which reduces its conformability to the area towhich it is applied.

Porous films are typically permeable to both liquid water and watervapor. They may be made by the incorporation of different organic orinorganic additives into a polymer film, the film then being stretchedor fillers removed therefrom chemically. Other conventional methodsinclude mechanical perforation and/or radiation techniques to form thedesired holes or slits in the polymeric film. Formation of uniform poresize in a film is very difficult, and porous plastic films are generallymore expensive than non-wovens.

On the other hand, non-porous barrier films are typically impermeable toboth liquid water and water vapor. As a result, using the impermeablefilm in a diaper backsheet, for example, makes the diaper hot beforeexposure to liquid (as the barrier film prevents air circulation) andclammy after exposure to moisture (because the barrier film precludesmoisture evaporation). Indeed, the use of an impermeable barrier film ina diaper may cause severe dermatological problems, such as skin rash oninfants, and skin sores on adults wearing such non-porous products.

It is also known to form a semi-porous barrier film of controlledporosity which is permeable to water vapor, but impermeable to liquidwater—that is, breathable. However, the method of manufacturing such amicroporous film of controlled porosity is typically complex andexpensive, and requires a relatively specialized polymeric input (forexample, conjugate fibers formed of two separately manufacturedpolymeric materials or laminates formed of two separately manufacturedpolymeric materials).

Clearly the need remains for a method of economically manufacturing amedia of controlled porosity, combining high vapor permeability and lowliquid permeability, without the use of chemical binders, additives orcoatings, from a single commercially available polymer. Such breathablemedia would find use in products which are sold in such quantity thatany reduction in the cost thereof (e.g., which makes it sufficientlyeconomical for manufacture for use in disposable products) is highlydesirable.

Accordingly, it is an object of the present invention to provide amethod of making of a media of controlled porosity, combining high vaporpermeability and low liquid permeability.

Another object is to provide such a method which does not require aspecialized polymeric input.

A further object is to provide such a method which does not require theuse of chemical binders, additives or coatings to provide the desiredpermeability or porosity.

It is also an object of the present invention to provide a material madeby the aforesaid method.

It is another object to provide such a material which does not producenoise during use and which exhibits cloth-like feel (hand).

It is a further object to provide such a material which is economical tomanufacture (e.g., for use in disposable products).

SUMMARY OF THE INVENTION

It has now been found that the above and related objects of the presentinvention are obtained in a method of making a non-woven fibrous mediacombining high vapor permeability and low liquid permeability. Themethod comprises the steps of providing a non-woven fabric formed fromfibers that are prematurely crystalized during web formation and have awide heat of fusion range distribution, and then calendering the fabricto soften the small polymer crystals therein of low heats of fusion, butnot the relatively larger crystals therein of relatively higher heats offusion, thereby to retain high vapor permeability.

The present invention additionally comprises a non-woven fibrous mediaproviding high vapor permeability and low liquid permeability. Thematerial is a non-woven fabric formed from fibers that are prematurelycrystalized polymer and have a wide heat of fusion range distribution.The fabric is calendered to soften the small polymer crystals therein oflow heats of fusion, but not the relatively large polymer crystalstherein of relatively higher heats of fusion, thereby to retain highvapor permeability while providing low liquid permeability.

In a preferred embodiment the polymer is polypropylene, and optimallyisotactic polypropylene, although other isotactic polymers may be used.The polymer is prematurely crystalized, preferably by quenching it priorto completion of fiber structural formation so that the polymer exhibitsa bell-shaped heat of fusion range distribution (prior to calendering).The temperature, pressure and roller speed of the calendering operationare selected to soften the small polymer crystals, but not therelatively larger polymer crystals. For example, the fabric ispreferably calendered at a temperature of about 25-110° C., a pressureof about 25-150 Newtons/mm, and a roller speed of up to 200meters/minute. The fabric is calendered to retain a moisture vaporpermeability of at least about 1200 g/m² @ 24 hours and to provide ahydrostatic head of at least about 10 millibars (about 100 mm H₂O). Thecalendered material may be made into a composite with, for example, atleast one spunbond, spunmelt or other nonwoven fabric layer.

BRIEF DESCRIPTION OF THE DRAWING

The above and related objects, features and advantages of the presentinvention will be more fully understood by reference to the followingdetailed description of the presently preferred, albeit illustrative,embodiments of the present invention when taken in conjunction with theaccompanying drawing wherein:

FIG. 1 is an isometric view of a fabric according to the presentinvention, laminated to a spunbond fabric, for use in a diaper; and

FIG. 2 is a flow chart of a preferred method of making the fabric.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing, and in particular to FIGS. 1 and 2thereof, the present invention relates to a method of making a non-wovenfibrous media of controlled porosity, generally designated by thereference numeral 10 the media combining high vapor permeability and lowliquid permeability. While for the purposes of the present invention,the media will be described as combining high water vapor permeabilityand low liquid water permeability, clearly the intended application ofthe media will dictate the specifics of these criteria—for example,whether the low liquid permeability applies to blood, bodily exudate orlike liquids and whether the high vapor permeability applies to watervapor, air or like gases. Typically, the goal is a substantially waterliquid impermeable and substantially water vapor permeable media. Theoptimum balance of properties can be tailored for individualapplications.

The molten polymer from which the media will be made is preferablyisotactic in nature so that it has a uniform structure over itspolymeric chain length. Alternatively, however, syndiotactic polymer maybe used in particular applications where the uniformity of the structureis of lesser importance. Atactic materials are not suitable for thepurpose of the present invention since the structure thereof is soirregular over its polymeric chain length that they strongly resistcrystallization. Polyolefins are preferred for use as the polymer,polypropylene being especially preferred. Thus, the preferred polymerfor use in the present invention is isotactic polypropylene.

Typically, pellets or other conventional forms of the polymer suitablefor handling within a manufacturing plant are placed in the hopper of aspinnerette and melted through an extruder. Once molten, the polymer isforced (extruded) through a spinnerette die defining small nozzlesthrough which the molten polymer passes, thereby forming fibers as thepolymer cools. For ease of processing, the polymer preferably has a veryhigh melt flow level rate and is collected from the spinnerette die atvery close die-collector distances. While the non-woven fabric ispreferably a meltblown, it may also be a spunbond or other non-wovenfibrous media to the extent that a suitable fabric is produced.

It is a feature of the present invention that the fabric be formed fromfibers that are prematurely crystalized during fabric formation. Suchprematurely crystalized fibers exhibit a “smectic” crystallinestructure. A smectic crystalline structure contains both small polymercrystals of low heat of fusion and relatively larger polymer crystals ofrelatively higher heats of fusion. The smectic crystalline structure isalso referred to as “paracrystallinity.”

The smectic or prematurely crystalized nature of the fibers useful inthe method of the present invention can be achieved in a variety ofdifferent ways. The most common technique is to quench the fibersemerging from the spinnerette die (e.g., with a cold gas or liquid, suchas air below 23° C.) before all of the polymer crystals in the fibershave grown to their full extent. As a result, the quenched fibers willcontain small polymer crystals of low heats of fusion and relativelylarger polymer crystals of relatively higher heat suffusion. In otherwords, prematurely crystalized fibers exhibit a wide range distributionof the heats of fusion.

That the polymer fibers exhibit a relatively wide heats of fusiondistribution is evidenced by the relatively broad bell-shaped curvedistribution observed in the DSC (Differential Scanning Calorimeter)data therefor. Typically a polymer exhibits a narrow heat of fusionrange distribution peak, indicating that all the polymer crystalsthereof are of roughly the same morphology—i.e., have comparable heatsof fusion so that they all soften at the same temperature. By way ofcontrast, smectic polymer contains some polymer chains that are highlycrystallized and other polymer chains that are less highly crystalized.As a result, the smectic polymer exhibits a relatively wide range ofheats of fusion, as evidenced by the relatively broad bell-shaped curvedistribution (as opposed to the narrow peak distribution of non-smecticpolymer). Indeed, the DSC curves for a smectic polymer typicallyindicate two peaks, a major peak and a minor peak within the major peak,while the DSC curves for a conventional non-smectic polymer exhibit onlya single peak.

At this juncture, it should be appreciated that the distinction betweenthe small polymer crystals and the relatively larger polymer crystals inthe smectic material reflects not a difference in the molecular weightsof the polymer crystals (i.e., the degree of polymerization thereof),but rather a difference in the morphology of the polymer crystalsthemselves. Typically the molten polymeric material which is passedthrough the spinnerette has polymer chains of generally the samemolecular weight. Even where the pellets themselves are characterized bya wide molecular weight range, the initial processing thereof by heatand pressure in the spinnerette hopper acts to make them of a generallyuniform molecular weight. Rather the “smectic crystallization” (or the“premature crystallization” or “supracrystallinity”), as applied to thepresent invention, relates to the morphology of the polymer crystals.

While various techniques may be used to achieve the prematurecrystallization of the fibers, it is most easily and economicallyachieved by rapid quenching of the fibers by liquid or gas cooling asthe fibers leave the die of the spinnerette and approach the web of thecollector. With the exception of the premature crystallization of thefibers during fabric formation, the production of the non-woven fabricaccording to the present invention is conventional in nature, andtypically reflects well known non-woven fabric production techniques,especially those used in the production of meltblown fabrics. The quenchtemperature at which the molten filaments are quenched will depend, tosome degree, on the composition of the molten polymer 30. For isotacticpolypropylene a quench temperature of 23° C. or below is preferred.

The non-woven fabric thus produced is then calendered to compact thesame. The roll surface temperature, roll surface pressure and roll speedof the calender are selected so as to soften the small polymer crystals(of relatively low heats of fusion), but not the relatively largerpolymer crystals (of relatively higher heats of fusion), thereby toretain high vapor permeability while providing low liquid permeability.For example, a preferred smectic polypropylene meltblown fabric iscalendered at a roll surface temperature of about 25-110° C., a rollsurface pressure of 25-150 Newtons/mm, and a roll speed of up to 200meters per minute to form a medium 10 of the present invention.

Roll speeds in excess of 200 meters per minute typically do not provideadequate time for heating of the fabric passing through the calendernip. On the other hand, roll speed should be maintained at as high alevel as possible in order to provide increased production rates.

Generally speaking, as the pressure and temperature of a calenderingoperation are increased, the crystallinity of the resultant medium (asmeasured by the increase of the area under the peaks of a DSC curve)also increases. If the temperature and pressure applied by the calendarare too low (or the roll speed too high), then the undercalenderedmeltblown fabric retains its high porosity to both liquid and gas andcannot act as a barrier sheet. If the temperature and pressure of thecalender are too high (or the roll speed too low), then theovercalendered meltblown fabric is converted into a film which istotally impermeable to both gas and liquid (and noisy in use as well).Clearly, the optimum temperature, pressure and roll speed will depend onthe nature of the particular smectic polymer being processed. While thedegree of vapor permeability and liquid impermeability (hydrohead) willvary with the particular intended application of the product, typicallya substantially complete liquid impermeability (even at a hydrostatichead of at least about 10 millibars) and a substantial complete vaporpermeability (that is, a vapor permeability of at least about 1200 g/m²@ 24 h) are preferred.

The preferred pressure and temperature parameters for the compactingstep may be easily and rapidly determined for any quenched material byholding one of the temperatures and pressures variables constant, whilevarying the other variable. Generally, the higher compactingtemperatures are required in order to obtain air permeabilities andMVTRs within the preferred ranges, and the higher compacting pressuresare required to obtain higher hydroheads.

It will be appreciated that air permeability and moisture vaportransmission rates are not necessarily related. Air permeability isclosely related to the compactness of the material being measured andits resistance to air flow therethrough, while MVTR is more related tothe morphology of the material being measured and its resistance tomoisture vapor transmission flow. Nonetheless, as a practical matter,air permeability measurements may be taken as indicative of MVTRmeasurements, subject to correction as necessary, where, for example,the MVTR measuring equipment is unavailable and the air permeabilitymeasuring equipment is available.

It is theorized that during calendering the small polymer crystals (withlow heats of fusion) soften and act as a binder between the unsoftenedlarger polymer crystals (with high heats of fusion). It is theorizedthat the softening of the small polymer crystals allows them to closethe pores between the large polymer crystals, thereby shrinking thefabric and forming a vapor permeable, liquid impermeable non-wovenbarrier medium. The calendering effects fiber shrinkage and contractionin the media, thereby closing the large liquid-bearing channels or porestherethrough while leaving open the relatively smaller vapor-bearingchannels or pores therethrough.

The optimum balance of properties can be tailored for particularapplications.

It will be appreciated by those skilled in the art that the term“calender,” as used herein, encompasses all means to perform both heattransfer and compacting (that is, heating and reducing the thickness ofa fabric). While a calender is the most common mechanism for performingthese operations, other mechanisms may be used instead or in additionthereto.

The media 10 is characterized by a hydrohead of at least about 10, andpreferably at least 20 millibars, an MVTR of at least about 1200, andpreferably at least 3000 g/m² @ 24 h, and an air permeability of about0.1-100, and preferably 0.4-3 cfm. The laminated composite 16 (formed ofthe media 10 and a spunbond fabric 12) suitable for use as a backsheetin a diaper or other absorbent product, has a hydrohead of at leastabout 20, and preferably 30 millibars, an MVTR of at least about 2000,and preferably 4000 g/m² @ 24 h, and an air permeability of about0.05-3, and preferably 0.1-1 cfm. These criteria are set forth in TableA below.

TABLE A HYDROHEAD MVTR AIR PERMEABILITY mbr g/m² @24 h cfm Media ≧10(≧20) ≧1,200 (≧3,000)  0.1-100 (0.4-3) Composite ≧20 (≧30) ≧2,000(≧4,000) 0.05-3 (0.1-1) Legend: (_) = preferred values

With regard to the data of Table A, it will be appreciated that theupper limits on the air permeability exists because, if material has toohigh an air permeability, it will probably leak liquid as well as air.While there is no upper limit set for the moisture vapor transmissionrate (MVTR), it is generally preferred that the MVTR not be so high asto produce a clammy feeling or chill due to a rapid evaporation of thewater.

No upper limits are given for the hydrohead because, as a practicalmatter, no liquid permeability is desired, regardless of the amount ofpressure being exerted on the liquid trapped by the media and/orcomposite. When the media and/or composite is used as the backsheet ofan infant diaper, the pressure exerted thereon (that is, primarily theweight of the infant) will be minimal so that the indicated minimalvalues of the hydrohead for the media/composite are acceptable. On theother hand, when the media/composite is used as the backsheet of anadult diaper or an adult incontinence pad, clearly a much higherhydrohead is required to prevent the escape of liquid under the weightof the adult. Thus, for example, hydroheads of 120 millibars would bethe minimum for a backsheet of an adult diaper intended for use by a 180lb. person. It will be appreciated that the infant/adult difference willalso play a role in the quantity of moisture (i.e., urine) which must beallowed to escape as moisture vapor, depending upon the size and healthof the kidneys of the wearer. The MVTR rates set forth are appropriatefor the accommodation of both infants and adults.

The products of the invention are characterized by a relatively hightensile strength (both MD and CD) relative to competitive products. Amedium 10 according to the present invention was laminated on one sideto a conventional spunbond fabric 12 and on the other side to aconventional meltblown fabric 14, to form a fabric 18 as illustrated inFIG. 1. The sample thus prepared had a hydrohead of 164 millibars and amoisture vapor transmission rate (MVTR) of 4411 g/m²/@24 h. In practicalterms, the specimen exhibited essentially no liquid leakage and a veryhigh moisture vapor permeability relative to other commercial diaperbacksheet specimens of comparable basis weight.

Referring now to FIG. 2 in particular, FIG. 2A illustrates the formationof a thermally sensitive meltblown smectic web and FIG. 2B illustratesthe compacting of the web and the optional lamination thereof to form anSM laminate 16.

Referring now to FIG. 2A in particular, the molten polymer 30 isextruded through a spinnerette or die hole 36 to form filaments 38. Atthe same time, hot air 40 is directed into the die body and emergesclose to the filaments 38 being formed (adjacent the spinnerette) todraw the molten filaments 38. The molten filaments are then immediatelyquenched via chilled air 41 (for example, at about or below 23° C.) asthey are fed into a quenching unit 42 via a fan 44 and piping 46 so thatthe drawn filaments 38 are prematurely quenched by the cold air, therebyresulting in the formation of a material containing both small polymercrystals and large polymer crystals. The prematurely quenched filaments38 then fall onto a collector 50 comprised of a roll or a conveyer belt52, under the influence of gravity and/or a suction box 54, to form athermally sensitive meltblown smectic web 56. The meltblown web 56 iseventually collected on a take-up roll 58 for storage or usedimmediately in the next step of the process.

Referring now to FIG. 2B in particular, a thermally sensitive meltblownsmectic web 56 is unwound from a supply drum 80A thereof at theunwinding station 80. The web is then passed through a compactingstation 82. The compaction calender 82A of compacting station 82 has tworolls. The top roller has a smooth steel outer surface and thermal oilheating so as to provide a controlled temperature at the calender nip.The bottom roll is made of a softer material as compared to steel (e.g.,a polyamide available under the trade name RACOLON) which make the mediasofter during compacting and prevents possible pinholes as the mediagets thinner. The simultaneous heating and compression of the fabricfibers by the compaction calender 82A imparts liquid impermeability(barrier properties) to the medium of the present invention whileretaining, at least to some degree, the gas permeability (breathability)thereof. The calendering effects fiber shrinkage and contraction in themedia, (due to the heat effect of calendering) thereby closing the largeliquid-bearing channels or pores therethrough while leaving open therelatively smaller vapor-bearing channels or pores therethrough. Theoutput of compacting station 82 is a media 10 according to the presentinvention.

However, to enhance the strength and feel thereof, the media 10 istypically laminated together with at least one spunbond, spunmelt orother nonwoven fabric on one side thereof, and optionally a meltblown orsecond spunbond, spunmelt or other nonwoven fabric on the other sidethereof. Thus, at unwinding station 82 a spunbond material 12 is unwoundfrom a supply drum 83A thereof. The compacted meltblown media 10 and thespunbond material 12 are laminated together at a laminating station 84by a lamination calender 84A to form a laminate 16.The laminationcalender has a rubber-covered steel roll adjacent the media and anengraved roller adjacent the spunbond material.

Special roll combinations in the laminating station 84 may be used toaffect the strength and textile-like softness (hand) of the finalproduct, as well as adding desirable patterns to the fabric foraesthetic reasons. Preferably, the final product 16 (or 18 if a thirdlayer is added) has a cloth-like feel combined with high tensile andrelated strength characteristics. The textile-like characteristics ofthe medium 10 are especially desirable where the fabric is used alone,although they may also be desirable when the medium 10 is used as anouter layer of a laminate.

In take-up station 85, the composite output 16 of lamination station 84is wound on a take-up roll 85A.

In the description above and the examples below, the important variableswere determined using internationally accepted tests as follows:

Hydrohead: EDANA-ERT-160-89

Air Permeability: EDANA-ERT-140.1-81

Mechanical (Tensile) Properties: EDANA-ERT-20.2-89

Basis Weight: EDANA-ERT-40.3-90

MVTR: ASTM-E96E

EXAMPLES Example I

In order to establish the porosity of a medium according to the presentinvention, a diaper backsheet made with a preferred product of thepresent invention was compared with the backsheets of severalcompetitive commercial diapers, with the results provided below in TableI.

The backsheet product of the present invention (labeled “FQF” inTable 1) was a SMM fabric containing on one side 10 g/m² of spunbondfabric, in the middle 10 g/m² of smectic media compacted according tothe present invention, and on the other side 10 g/m² of uncompressedmeltblown fabric, for a total of 30 g/m². It was tested against diaperbacksheets used in competitive commercial diapers available under thetrade names HUGGIES/ULTRATRIM, HUGGIES/SUPREME, PAMPER/PREMIUM andDRYPERS/SUPREME.

All specimens were tested for hydrohead, MVTR, tensile strength (MD andCD) and percent elongation (MD and CD), and the data recorded in TableI.

The measurement of MVTR was accomplished by monitoring the amount ofdistilled water that evaporated through the specimen over a 24 hourperiod. The temperature of the water was maintained at 38° C. by using aconstant temperature bath in which the jars of water were placed. A fanwas used to maintain a constant air flow over the specimen. The heightof the liquid was such that it did not interfere with the measurement asthe top of the liquid was sufficiently above the bottom of the specimen.

The data of Table I shows that the hydrohead of a diaper backsheet madewith the media according to the present invention (164) was second onlyto the Pamper/ Premium (192), and that the MVTR and percent elongationthereof (MD and CD) according to the present invention (164) exceededall others. The tensile strength (MD and CD) of the media compositeaccording to the present invention were comparable to those of thecompetitive products.

The data illustrate that a backsheet incorporating the media of thepresent invention as the barrier layer is comparable, or superior, tocompetitive products in all pertinent respects and, in particular, isgreatly superior with respect to MVTR. Indeed, the MVTR of a backsheetaccording to the present invention is at least twice as high as the MVTRof the backsheets of the commercial products tested.

Example II

Three specimens were prepared from identical polypropylene pelletsuseful in the present invention. The first specimen was processedaccording to the present invention, including quenching and compacting.The second specimen was processed in the same manner, except that thequenching step and the compacting step were omitted. The third specimenwas similarly processed, but with the quenching step being included andonly the compacting step being omitted. The fourth and fifth specimenswere similarly processed, but with the compacting step being includedand only the quenching step being omitted. The fourth specimen wascompacted at 75 N and 100° C., while the fifth specimen was compacted at150 N and 110° C.

Pertinent data was collected at various points in the processing asreported in Table II below.

As might be expected, the material of specimen 2, a common meltblown,exhibited an air permeability of about 193 cfm, higher than the 100 cfmupper limit of acceptability. Similarly, the material of specimen 5,quenched and compacted at a high temperature, was a rigid, brittle filmexhibiting a low hydrohead of 8 mm H₂O, relative to the lower limit of10 cm H₂O (10 millibars) for acceptability. Specimens 3 and 4 exhibitedrelatively high air permeabilities (83 cfm for specimen 3 and 36 cfm forspecimen 4) such that they were within the limit for media according tothe present invention as broadly defined (0.1-100 cfm), butsubstantially higher than the preferred limit (0.4-3 cfm). Furtherspecimen 4 exhibited an unacceptably low MVTR, while specimens 3 and 5were so porous to moisture vapor as to be out of the range of theavailable MVTR tester used.

The data illustrate that the quenching step alone or the compacting stepalone are insufficient to produce a preferred medium according to thepresent invention. A preferred medium according to the present inventionresults only when both the quenching step and the compacting step areboth performed.

The products of the present invention find utility in the healthcareindustry, as discussed previously, as well as such diverse fields asclean room and health care gowns, clean room filters, house wraps,sterile packaging, battery separators and other industrial applicationswith barrier requirements which can be met by the product of the presentinvention.

For those applications which require a more elastomeric and moredrapable media, without any change in the barrier properties or otheradvantages of the present invention, the molten polymer from which themedia of the present invention is preferably made from a blend of 60-90%polypropylene and 10-40% polybutylene by weight. Media made from such ablend exhibit a higher elongation to break and are much more drapable ascompared to those made from 100% polypropylene. Since such media aremore elastic and behave more like rubber, laminates using such mediaexhibit lower noise (that is, less crinkling). A preferred polybutylenefor use in the present invention is available under the trade name PB DP8910PC from Montell Chemical Co.

It will be appreciated by those skilled in the art that the hydroheadtest is of a static nature and measures only the ability of the barriermedia to withstand a water pressure gradually applied thereto; this issufficient for many applications. However, certain applications requirea more dynamic test to determine the capacity of the barrier media towithstand an impact suddenly driving the water thereagainst. The dynamicliquid impact test mimics the dynamic load/area (energy) that a babywill impart to a saturated core/backsheet structure when abruptly goingfrom a standing to a sitting position. The dynamic liquid impact (ing/m²) is calculated based on the impact energy that an average 20 lb.baby will impart to a saturated diaper if the baby “falls” onto it froma standing position. The baby is modeled as two rigid links of knownmass and length, and the assumption is made that the links “fall” fromrest, with the impact area being the region under the diaper. This worksout to be approximately 20 Joules (14.75 ft.-lb.) over an average baby“seat” area of 13.5 in.² or about 2300 J/m². Dynamic liquid impact wasmeasured according to a proprietary Dynamic Liquid Impact Test MethodV-L-35 of Proctor & Gamble.

A single layer of non-porous film alone gives a test result of 0 g/m². Asingle layer of laminate using a media according to the presentinvention gives a test result of 547 g/m². A sample of two layers ofsuch laminate gives a test result of 375-465 g/m².

For a diaper backsheet, test results of less than 700 g/m², preferablyless than 550 g/m², are acceptable on a 30 gsm laminate sampleconsisting of a spunbond layer (10 gsm), a central layer of mediaaccording to the present invention (10 gsm), and a meltblown layer (10gsm) laminate.

Thus, the media of the present invention exhibits acceptable testresults on a dynamic impact liquid test. The dynamic impact liquid testresults confirm that the media of the present invention is the limitingfactor.

A sample made of two laminates (for example, each laminate having themedia of the present invention in the center, a spunbond on one sidethereof, and a meltblown on the other side thereof) typically exhibits alower dynamic impact liquid test level than a sample made of a singlelaminate alone. It is theorized that this is due to the increasedcalendering of the media layers in the laminate affecting the morphologyof the test material.

To summarize, the present invention provides a method of making a mediaof controlled porosity, combining high vapor permeability and low liquidpermeability, which method does not require a specialized polymericinput or the use of chemical binders, additives or coating to providethe desired permeability. The present invention also provides materialmade by the aforesaid method, such material not producing noise duringuse, exhibiting cloth-like feel (hand), and being sufficientlyeconomical to manufacture for use in disposable products.

Now that the preferred embodiments of the present invention have beenshown and described in detail, various modifications and improvementsthereon will become readily apparent to those skilled in the art.Accordingly, the spirit and scope of the present invention is to beconstrued broadly and limited only by the appended claims, and not bythe foregoing specification.

TABLE I Huggies/ Huggies/ Pamper/ Drypers/ Ultratrim Supreme PremiumSupreme FQF Hydrohead 110 72 192 69 164 (mbar) MVTR 1495.5 1944.1 1198.41046.8 4411 g/m²/24 hrs MD 53.14 46.32 71.18 47.6 80.23 Tensile (N) CDTensile 19.98 45.15 17.52 23.07 43.23 (N) MD Elong 30.4 53.6 107.13 5240.85 % CD Elong 40.36 30.11 132.18 54.37 62.92 %

TABLE II Hydrohead MVTR Air Permeability Specimen mbar g/m² @ 24 hr cfm1 59^(A) 4187 0.5 2 29^(A) — 193 3 40^(A) — 83 4 70^(C) 1148 36 5  8^(C)— 1 Legend = ^(A)Test head size 28 cm² ^(B)Test head size 38 cm²^(C)Test head size 5 cm²

I claim:
 1. A method of making a non-woven fibrous media combining highvapor permeability and low liquid permeability, the method comprisingthe steps of: (A) providing a non-woven meltblown fabric formed offibers that have small polymer crystals therein of low heats of fusionand relatively larger polymer crystals therein of relatively higherheats of fusion, the fibers being formed of a polymer drawn and thenprematurely crystallized by premature quenching with a stream of coldquench air immediately after drawing prior to completion of fiberformation to form both small polymer crystals therein of low heats offusion and relatively larger polymer crystals therein of relativelyhigher heats of fusion, and then collected during fiber collection toform the fabric; and (B) calendering the fabric at a roll surfacetemperature of 25-110° C., a nip linear force of about 25-150Newtons/mm, and a roll speed of up to about 200 meters/minute, thetemperature, pressure and roll speed of the calendering operation beingcooperatively selected to soften the small polymer crystals therein ofrelatively higher heats of fusion, thereby to retain a high vaporpermeability, of at least about 1200 g/m² @24 h, while providing a lowliquid permeability as measured by a hydrohead of at least about 10millibars, through compaction, fiber shrinkage and contraction in thefibrous media.
 2. The method of claim 1 wherein the polymer isisotactic.
 3. The method of claim 1 wherein the polymer ispolypropylene.
 4. The method of claim 1 wherein the polymer is a blendof polypropylene and polybutylene.
 5. The method of claim 4 wherein theblend is 60-90% polypropylene and 10-40% polybutylene by weight.
 6. Themethod of claim 1 wherein the polymer is isotactic polypropylene.
 7. Themethod of claim 1 wherein the polymer is prematurely crystallized byquenching thereof prior to completion of fiber formation.
 8. The methodof claim 1 including the step of forming a composite of the calenderedmaterial with at least one nonwoven fabric layer.
 9. The method of claim8 including the step of forming a composite of the calendered materialwith at least one spunbond fabric layer.
 10. The method of claim 1wherein the fabric is calendered between a smooth hard roll and a softerroll to effect compaction, fiber shrinkage and contraction in thefibrous media.
 11. A method of making a non-woven fibrous mediacombining high vapor permeability and low liquid permeability, themethod comprising the steps of: (A) providing a non-woven meltblownfabric formed of fibers that have small polymer crystals therein of lowheats of fusion and relatively larger polymer crystals therein ofrelatively higher heats of fusion, the fibers being formed of a polymerof isotactic polyprolene, drawn and then prematurely crystallized bypremature quenching with a stream of cold quench air immediately afterdrawing prior to completion of fiber formation to form both smallpolymer crystals therein of low heats of fusion and relatively largerpolymer crystals therein of relatively higher heats of fusion, and thencollected during fiber collection to form the fabric; and (B)calendering the fabric at a roll surface temperature of 25° to less than80° C., a nip linear force of about 25-150 Newtons/mm, and a roll speedof up to about 200 meters/minute, the temperature, pressure and rollspeed of the calendering operation being cooperatively selected tosoften the small polymer crystals therein of low heats of fusion, butnot the relatively larger polymer crystals therein of relatively higherheats of fusion, thereby to retain a high vapor permeability, of atleast about 1200 g/m² @24 h, while providing a low liquid permeabilityas measured by a hydrohead of at least about 10 millibars, throughcompaction, fiber shrinkage and contraction in the fibrous media.